1. Field of the Invention
The present invention relates to a color picture tube provided with a residue electron removing assembly, and particularly to a color picture tube in which there is provided a residue electron removing assembly functioning as a bridge for discharging residue electrons which land on a phosphor plated screen and those remaining on a shadow mask, as electrons emitted form an electron gun pass through the color sorting shadow mask to the phosphor plated screen.
2. Description of the Related Art
Generally, in a shadow mask type color picture tube, electron beams emitted from an electron gun cross one another at numerously large number of holes formed on a shadow mask. The beams collide with aligned phosphor dots (or stripes) so that he phosphor plated screen produces the three basic colors.
In such an electron irradiating operation, the brightness of the luminescent color phosphors on the conductive layer is determined by the intensity of the electron beams emitted by an electron gun. When the electron beams collide with the phosphors, if the electron beams land on a periphery of the phosphors or near a black matrix, there occurs a negative charge repulsion phenomenon. This results in residue charges being formed between the shadow mask and the phosphors. These residue charges make the image on the screen appear severely unstable and unclear. A circular strip may also be seen on the image.
Further, as the light emitting condition of the image deviates from its normal state, a phenomenon where a beam path is deflected as it travels through the shadow mask, (i.e., a regrouping phenomenon) is generated.
In an attempt to overcome the above described disadvantages, a structure as shown in FIG. 1 has been proposed. A first graphite layer 6 is formed between stud pin 7 and aluminum layer 5, with stud pin 7 being fixedly secured on one side of the inner face of panel 1. Aluminum layer 5 is coated on phosphor layer 4 of panel 1. A frame 10 which supports opposite sides of shadow mask 9 is fixedly secured on stud pin 7 through hook spring 8. Inner shield 12 which is disposed within the color picture tube is fixed to frame 10 by means of clip 11. One end of contract spring 13 is secured to inner shield 12 by spot-welding thereto and the other end of the contact spring 13, which is bent, is made to elastically abut on second graphite layer 14 which is coated on an inner face of funnel 2.
In the above conventional structure, residue electrons which remain on shadow mask 9 after failing to pass the shadow mask 9, flow through frame 10 (or inner shield 12), to contact spring 13, and to second graphite layer 14. Similarly, residue electrons remaining after collision with phosphor layer 4, flow through aluminum layer 5, to first graphite layer 6, to stud pin 7, to hook spring 8, to frame 10, to contact spring 13, and to second graphite layer 14 to the outside of funnel 2. Thus, contact spring 13 serves as a bridge such that residue electrons are discharged from shadow mask 9 through frame 10 to inner shield 12 and finally to the outside.
First graphite layer 6 serves as a bridge such that residue electrons are discharged from phosphor layer 4 through aluminum layer 5, to hook spring 8, to frame 10 and to contact spring 13 to the outside. In the above conventional structure, the major disadvantage lies in that the transfer path for residue electrons consists of an assembly having a large number of components.
Furthermore, when forming first graphite layer 6 which acts as a bridge, a graphite slurry is spread by way of a brush or the like between aluminum layer 5 (coated on phosphor layer 4) and stud pin 7 (fixed to the inner face of panel 1). The spread graphite slurry is then dried. However, in spreading the graphite slurry, the graphite slurry not only can intrude into the fluorescent effective area of aluminum layer 5, but the graphite slurry can also be detrimentally sprinkled by careless manipulation of the brush.
In securing contact spring 13, contact spring 13 is to be spot-welded, for best operation, to inner shield 12 at least on 4 spots, and wherein inner shield 12 is secured to frame 10 by means of clip 11. However, in performing the necessary spot-weldings, spark particles remain within a picture tube, and these particles can block the holes of shadow mask 9.
Further, there are also other proposed structures such as the color picture tube manufacturing process of Japanese Patent Laid-open No. SHOWA 60-70640, and the color picture tube assembly of Japanese Patent Laid-open No. SHOWA 61-237339. In these references, there is shown a contact spring which is directly spot-welded to the frame, or secured by means of a clip, and the leading end of the contact spring is elastically contacted to the second graphite layer of the panel. When spot-welding is necessary, the above described spark particle drawback remains and can block the holes in the shadow mask. Similarly, since a clip is used, the problem of non-economic multiple components still exists.
U.S. Pat. No. 4,829,212 proposes yet another structure which is to be described below. That is, the electrical connecting assembly of the interior of a CRT, a known construction, is constituted such that one side of the conductive layer of the panel is connected through a contact spring to the stud pin, so that the contact spring should simply electrically connect the shadow mask to the conductive layer of the panel. In this construction, however, there arises the problem that some additional means has to be provided in order to discharge the residue electrons to the outside.